Reality bites was Re: Step count / inch problem

Carlos,

Thank you.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., "Carlos Guillermo" <carlos@v...> wrote:
> Hi Ballendo -
>
> The Thomson rolled ballscrew literature shows a graph of the type
> of variation you are likely to see with their ballscrews. They
> clearly show that the errors DO stack up for longer lengths (they
> refer to the "Cumulative Representative Lead"), and they also show
> the superimposed error component that is cyclical, like what you
> describe ("Lead Fluctuation"). The graph is of a sloped line,
> with waviness added. Just imagine taking a ballscrew with
> cyclical errors, and changing its temperature. The overall length
> will change, and every point along the way will shift
> proportionally (with even temperature changes), but the cyclical
> errors will still be there. The cyclical errors are in fact small
> compared to the cumulative errors. It's just part of the
> manufacturing process. I spoke to a Thomson engineer who said if
> you could use software to factor out this cumulative error, you'd
> compensate for the majority of the error. When they give
> accuracies of .004"/ft, they're mostly talking about the
> cumulative errors. I tried to get some numbers on the cyclical
> errors with no luck. I believe they will map out their more
> pricey ballscrews for a fee, however. Anybody have this kind of
> data? It would be interesting to compare the magnitude of the
> cyclical variations against the cumulative errors, and to see the
> error characteristics of an actual ballscrew (slope, waviness,
> arcing, etc)
>
> HTH,
>
> Carlos Guillermo
> VERVE Engineering & Design
>
> Ballendo wrote:
> <snip>
> Ballscrew errors, even with the cheapies, do not usually stack
> up; but instead are cyclical variations within shorter distances.
>
> <snip>